Technical Field
[0001] The present invention relates to a gas generator used in a restraining device for
vehicles such as an airbag apparatus.
Description of Related Art
[0002] Some of gas generators for deploying an airbag have an elongated cylindrical housing
because of their attachment position. In such gas generators, an igniter is attached
to one end thereof and a gas discharge port is provided on the other end.
[0003] When the igniter is separated from the gas discharge port in this manner, a lead
wire connected to the igniter does not become an obstacle at the time of attaching
an airbag around the gas discharge port, which is advantageous because the attachment
to a vehicle is facilitated.
[0004] However, with the igniter provided at one end, when ignition of a gas generating
agent progresses from one end to the other end, the gas generating agent ignites easily
in some positions whereas it does not easily ignite in some other positions.
[0005] In a gas generator 10 disclosed in
US-B No. 7,073,820, an igniter 20 is disposed in one end of an elongated housing 12, and a gas generating
agent 30 is charged around the igniter 20.
[0006] A chamber in which the igniter 20 is disposed and the gas generating agent 30 is
filled and a chamber 21 in which another gas generating agent 99 is filled are partitioned
by a spacer 18 provided with a communication hole 19 in a central portion thereof.
The communication hole 19 is closed by a seal 97.
[0007] Moreover, since the igniter 20 is disposed in such a state that an ignition portion
protrudes into a combustion chamber, a pocket-like annular space is formed near an
end closure 22 and the gas generating agent 30 is also present in the annular space.
[0008] Fig. 1 of
JP-A No. 2011-157025 shows a gas generator that includes a first porous plate member 14 and a second porous
plate member 32.
SUMMARY OF INVENTION
[0009] The present invention provides a gas generator including
a cylindrical housing with an ignition device attached at one end and a diffuser portion,
which has a gas discharge port, attached at the other end,
a first combustion chamber formed inside the cylindrical housing at the one end to
which the ignition device is attached, being defined by a first porous plate member,
and being charged with a molded article of first gas generating agent,
a second combustion chamber formed in the cylindrical housing and defined by a second
porous plate member, which is disposed axially at a distance from the first porous
plate member and has a second through hole, the second combustion chamber being charged
with a molded article of second gas generating agent,
the ignition device provided by fixing an igniter main body with a columnar ignition
portion, to a fixing member including an igniter collar, the ignition portion disposed
to protrude inside the first combustion chamber,
the first porous plate member having first through holes, a proportion of a first
total opening area of only outer first through holes arranged in the vicinity of a
peripheral edge portion and in a circumferential direction of the first porous plate
member to a total opening area of the first through holes in the first porous plate
member being not less than 95%,
axial end surfaces of the first combustion chamber respectively formed by the first
porous plate member, and the ignition portion of the igniter and the igniter collar,
an annular space formed between an outer peripheral surface of the ignition portion
and an inner peripheral wall surface of the cylindrical housing, which radially faces
the outer peripheral surface of the ignition portion, the annular space having a bottom
surface defined by the igniter collar,
a height (H) of a top surface of the ignition portion from the bottom surface and
a smallest length (Lmin) of the molded article of the first gas generating agent charged
in the first combustion chamber satisfying a relation of Lmin<H, and
an axis X of the cylindrical housing being coincident with a central line of the ignition
portion of the igniter main body, the first porous plate member, and the second porous
plate member.
BRIEF DESCRIPTION OF DRAWINGS
[0010] The present invention will become more fully understood from the detailed description
given hereinbelow and the accompanying drawings which are given by way of illustration
only, and thus are no limitative of the present invention and wherein:
[0011]
[Fig. 1] Fig. 1 shows a cross-sectional view in the axial direction of a gas generator
according to the present invention;
[Fig. 2] Fig. 2 shows a partial enlarged view of Fig. 1;
[Fig. 3] Fig. 3 shows a diagram illustrating an arrangement of through holes in a
first porous plate member;
[Fig. 4] Fig. 4 shows a perspective view of a molded article of a gas generating agent
charged in a first combustion chamber;
[Fig. 5] Fig. 5 shows a diagram for describing a charging state of the molded article
of the gas generating agent in the first combustion chamber; and
[Fig. 6] Fig. 6 shows a diagram illustrating an arrangement of through holes in a
second porous plate member.
DEATILED DESCIRPITON OF INVENTION
[0012] In
US-B No. 7,073,820, since the ignition portion of the igniter 20 is disposed to face the communication
hole 19, a combustion product generated due to activation flow linearly through the
communication hole 19 to the adjacent chamber 21. As a result, the gas generating
agent present in the pocket-like annular space may not be easily ignited.
[0013] If the ignition of the gas generating agent 30 in the annular space is delayed or
the gas generating agent 30 is remained without burning out, designed performance
is not obtained.
[0014] Although it is described in
JP-A No. 2011-157025 that the first porous plate members 14 and the second porous plate member 32 includes
a plurality of holes, there is no description as to a hole arrangement.
[0015] In Fig. 1, when compared with the configuration in
US-B No. 7,073,820, an ignition portion 16a of an igniter 16 protrudes relatively in a small distance,
hence a pocket-like annular space, like a gas generator 10 disclosed in
US-B No. 7,073,820, is not formed substantially. Due to this, although it is unlikely occurred that
ignition is delayed in the first combustion chamber 20 including the igniter 16, a
gas generating agent, disposed away from the discharge direction of the combustion
products generated from the ignition portion 16a, is not easily ignited.
[0016] The present invention is to provide an elongated gas generator capable of burning
out an entire molded article of the gas generating agent as designed even when a pocket-like
annular space, in which the molded article of the gas generating agent is present,
exists around an igniter.
[0017] The first combustion chamber is formed by being surrounded by the cylindrical housing,
the first porous plate member, and the ignition device (the igniter and the igniter
collar).
[0018] In the invention, the first through holes contain plural holes connecting the inside
of the first combustion chamber with an outside thereof. The outer first through holes
are provided at a peripheral edge and arranged in the circumferential direction of
the first porous plate member.
[0019] The first porous plate member has preferably first through holes consisting of only
outer first through holes arranged in the circumferential direction and provided only
in the vicinity of the peripheral edge portion thereof. The first through holes may
also be formed in a portion excluding the portion in the vicinity of the peripheral
edge portion. The outer first through holes are through holes corresponding to those
in the outermost position of the first porous plate member. The first through holes
may be closed by a seal tape.
[0020] In this case, the proportion of the first total opening area of only the outer first
through holes in the vicinity of the peripheral edge portion to the total opening
area of the first through holes of the first porous plate member is not less than
95%, and preferably not less than 98%, and more preferably 100%.
[0021] When "r" is the radius from the central point (where the axis X of the cylindrical
housing passes) of the first porous plate member (circular) to the circumference thereof,
it is preferable to set a position of each of the first through holes in the vicinity
of the peripheral edge portion such that a distance from the peripheral edge portion
to the centers of the respective through holes is preferably within 0.2r (within 20%
of the radius r) and more preferably within 0.15r (within 15% of the radius r).
[0022] In the ignition device, the igniter main body including the ignition portion is fixed
by the fixing member including the igniter collar, and the ignition portion is disposed
to protrude into the first combustion chamber.
[0023] Thereby, the pocket-like annular space whose bottom surface is the igniter collar
is formed between the outer peripheral surface of the ignition portion protruding
into the first combustion chamber and the inner peripheral wall surface of the cylindrical
housing.
[0024] The first gas generating agent includes a plurality of gas generating agent bodies
or articles. When the first gas generating agent is charged in the first combustion
chamber, some of the bodies or part of the body is disposed in the pocket-like annular
space.
[0025] When the molded article of the first gas generating agent is charged in the first
combustion chamber during the manufacturing process of the gas generator, a required
amount of the molded article of the first gas generating agent is poured into the
space (the first combustion chamber) serving as a combustion chamber in such a way
that the molded articles of the first gas generating agent are not aligned.
[0026] Thus, when the molded article of the gas generating agent is cylindrical, for example,
the molded article of the gas generating agent is loaded in various orientations,
and a gap is present between the adjacent molded articles of the gas generating agent.
[0027] After that, an operation to eliminate the gap such as applying vibration from the
outside is performed. Then, the molded article of the gas generating agent is pressed
from both side in the axial direction by the fixing member (in the present invention,
the first porous plate member and the ignition device) to closely fix the molded article
of the gas generating agent without the gap.
[0028] The molded article of the gas generating agent is charged in this manner, some molded
article of the gas generating agent may be positioned, in the annular space, within
an area lower than the height (H) of the top surface, of the columnar ignition portion
(only in the side of the igniter collar), although it is not possible to check the
charging state of the molded article of the gas generating agent after charging. That
is, with Lmin>H, the molded article of the gas generating agent protrudes out of the
annular space. However, with Lmin<H, in some charging states, some of the molded article
of the gas generating agent may be confined in the annular space, within an area lower
than the height (H) of the top surface of the columnar ignition portion.
[0029] Here, the smallest length (Lmin) of the molded article of the gas generating agent
is a diameter when the molded article of the gas generating agent is columnar, and
is the thickness when the molded article of the gas generating agent is disk-shaped,
for example.
[0030] When the igniter is activated and the combustion product is discharged from the ignition
portion, including the cases of being discharged axially or radially, the combustion
product is discharged forward, further than the ignition portion (the top surface
of the ignition portion).
[0031] In this case, if a portion including the central portion (the portion coincident
with the axis X) of the first porous plate member is open widely (or opened widely
by rupture of the seal tape), most of the combustion products from the ignition portion
are directly discharged outside the first combustion chamber, there may be occurred
that the molded article of first gas generating agent charged in the pocket-like annular
space of the first combustion chamber is ignited with delay, or not burn up completely.
[0032] However, in the present invention, since most through holes are formed in the vicinity
of the peripheral edge portion of the first porous plate member, most of the combustion
product, discharged from the ignition portion, collides the first porous plate member
(the portion where less number of first through holes is formed or no first through
holes are formed) and is diffused inside the first combustion chamber (the combustion
product also reaches the pocket-like annular space by deflection).
[0033] Therefore, when the relation of Lmin<H (preferably H/Lmin = 2 to 5) is satisfied,
even when there are a lot of molded articles of the gas generating agent charged,
in the annular space, within an area lower than the height (H) of the top surface
of the columnar ignition portion, all of the molded article of first gas generating
agent charged in the pocket-like annular space of the first combustion chamber is
ignited easily, and delayed ignition or incompletion of combustion will not occur.
[0034] It is preferable in the gas generator of the present invention that the first porous
plate member has the first through holes consisting of only the outer first through
holes formed in the circumferential direction and only in the vicinity of the peripheral
edge portion thereof.
[0035] It is preferable that the present invention provides a gas generator according to
the invention, wherein
a ratio (a2/a1) of a total opening area (a2) of the second through hole formed in
the second porous plate member and a total opening area (a1) of the first through
holes formed in the first porous plate member is between 0.9 and 1.2.
[0036] The combustion gas, generated by combustion of the molded article of first gas generating
agent in the first combustion chamber, flows into the space (a combustion gas migration
space) between the first porous plate member and the second porous plate member and
then flows into the second combustion chamber through the through holes of the second
porous plate member.
[0037] In this case, when a2/a1 satisfies the above, the migration of the combustion gas
from the through holes of the first porous plate member to the combustion gas migration
space and from the combustion gas migration space to the through holes of the second
porous plate member is preferably more accelerated.
[0038] It is preferable that the present invention provides a gas generator according to
the invention, wherein
a cylindrical member provided with a communication hole in a peripheral wall portion
is further disposed in the second combustion chamber,
the cylindrical member is disposed so as to form a gap between an inner peripheral
wall surface of the cylindrical housing and the peripheral wall portion of the cylindrical
member, and
the cylindrical member has a first opening end, preferably having an enlarged diameter
portion and an outer peripheral edge, on a side of the second porous plate member,
that abuts against the inner peripheral wall surface of the cylindrical housing, and,
at the opposite side, a second end, preferably having a bottom surface and a central
hole at a center thereof, that is supported on a side of the diffuser portion.
[0039] The cylindrical member has the communication hole (preferably, a plurality of communication
holes) in the peripheral wall portion, and is preferably formed of an elastic metal.
The communication hole may be formed in the peripheral wall portion of the cylindrical
member axially and circumferentially at equal intervals. Moreover, the communication
holes may be unevenly distributed on the cylindrical member nearer to the diffuser
portion, and in this case, the number and diameter of the communication holes are
adjusted so that the opening area in the diffuser portion side increases.
[0040] The cylindrical member is disposed to form a gap (a cylindrical gap) between the
cylindrical member and the inner peripheral wall portion of the cylindrical housing,
and has the first opening end, that abuts against the inner peripheral wall surface
of the housing and faces one end (on the side of the ignition device) of the housing,
and the second end supported on the side of the diffuser portion.
[0041] In order to form the gap between the cylindrical member and the inner peripheral
wall surface of the cylindrical housing, the outer diameter (the outer diameter of
the peripheral wall portion) of the cylindrical member is set to be smaller than the
inner diameter of the cylindrical housing.
[0042] The cylindrical member is provided with the communication hole formed in the peripheral
wall portion, and the inside of the cylindrical member (the second combustion chamber)
and the cylindrical gap communicate with each other through the communication hole.
[0043] When the cylindrical gap is formed, the cylindrical gap serves as a discharge passage
for combustion gas flowing to the diffuser portion when an inflator is activated.
[0044] While the combustion gas flows through the cylindrical gap toward the diffuser portion,
the combustion gas easily comes into contact with the cylindrical member (the peripheral
wall portion) and the inner peripheral wall surface of the cylindrical housing, which
define the gap. As a result, functions of collecting residues and cooling the gas
are improved.
[0045] In addition, since the gas flowing through the cylindrical gap reaches the gas discharge
port without being obstructed, the period of time from ignition to gas discharge is
preferably reduced.
[0046] It is preferable that the present invention provides a gas generator according to
the invention, wherein
the cylindrical member includes an enlarged diameter portion in which a diameter of
an opening portion on a side of the first opening end is enlarged and a central hole
formed at a center of a bottom surface on a side of the second end,
a cup-like shaped gas diverting member having a communication hole in a peripheral
wall portion and a projection on a bottom surface, is disposed on the side of the
diffuser portion, and has an opening arranged to face the diffuser portion,
the first opening end of the cylindrical member abuts against the inner peripheral
wall surface of the cylindrical housing, and
the central hole of the cylindrical member is fitted to the projection on the bottom
surface of the gas diverting member.
[0047] The cylindrical member has an enlarged diameter portion in which a diameter of the
opening portion on the side of the first opening end (that is, on the side of the
ignition device and the first combustion chamber) is enlarged, and the enlarged diameter
portion abuts against the inner peripheral wall surface of the cylindrical housing.
Before the cylindrical member is disposed into the cylindrical housing, the outer
diameter of the enlarged diameter portion is, for example, adjusted to be slightly
larger than the inner diameter of the cylindrical housing. Thereby, the enlarged diameter
portion and the inner peripheral wall surface of the cylindrical housing tightly abut
against each other (press against each other to be in close contact).
[0048] As a result, the cylindrical member is tightly fixed and the cylindrical gap (in
particular, the cylindrical gap having an even width) is easily obtained. In addition,
since the combustion products from the molded article of second gas generating agent
is prevented from short-passing into the cylindrical gap, the ignition ability of
the entire second gas generating agent is improved.
[0049] The cylindrical member has the central hole at the center of the bottom surface on
the side of the second opening end (that is, on the side of the diffuser portion).
[0050] The gas diverting member has a cup-like shape and has a communication hole in a peripheral
wall portion and a projection at the bottom surface, projecting toward the second
combustion chamber. The gas diverting member is disposed so that the opening portion
thereof faces the diffuser portion. The gas diverting member is disposed such that
the central axis thereof is coincident with the central axis of the diffuser portion
and the central axis of the cylindrical housing.
[0051] The projection on the bottom surface of the gas diverting member is fitted into the
central hole of the cylindrical member on the side of the second end. Thereby, fixing
of the cylindrical member at the second end and forming the cylindrical gap (in particular,
the cylindrical gap having a constant width) is easily obtained. Furthermore, when
the cylindrical member is fixed in this manner, by arranging the central axes of the
diffuser portion, the cylindrical housing and the gas diverting member to be coincided
with each other, these central axes can be easily coincided with the central axis
of the cylindrical member.
[0052] It is preferable that the present invention provides a gas generator according to
the invention, wherein
the first porous plate member has the first through holes consisting of only the outer
first through holes arranged in the circumferential direction only in the vicinity
of the peripheral edge portion thereof, and
the second porous plate member has a plurality of second through holes consisting
of only outer second through holes arranged in the circumferential direction only
in the vicinity of the peripheral edge portion thereof.
[0053] By using the cylindrical member and a combination of two porous plate members having
the through holes only in the vicinity of the peripheral edge portion, it is possible
to quickly open the gas discharge passage.
[0054] According to the gas generator of the present invention, the ignition portion of
the igniter is disposed to protrude into the combustion chamber. Thus, even when a
pocket-like annular space is formed in the combustion chamber, the entire molded article
of the gas generating agent is not ignited with delay and burnt up completely regardless
of the charging state of the molded article of the gas generating agent.
DESCRIPTION OF EMBODIMENTS
[0055] An embodiment of the present invention will be described with reference to Figs.
1 to 5.
[0056] An igniter 16 which is an ignition device is attached to one end 10a of a cylindrical
housing 10.
[0057] In the igniter 16, an igniter main body including an ignition portion 18, which is
a known electric igniter, is fixed to a metallic collar 17 serving as a fixing member.
The center (the center of a top surface 18a of the ignition portion 18) of the ignition
portion 18 is coincident with the central axis X of the cylindrical housing 10.
[0058] The igniter 16 may be fixed to the metallic collar 17 in such a state that part of
the ignition portion 18 including an ignition charge is coated with a resin.
[0059] As the igniter 16, for example, as illustrated in Fig. 2 of
JP-A No. 2001-165600, an initiator assembly 28, in which an initiator 32 is surrounded by a collar assembly
31 (a resin portion 36 and a metallic collar 40) and an ignition portion (an ignition
charge 62 and a charge holder 64 surrounding the ignition charge 62) protrudes from
the resin portion 36, may be used.
[0060] A first porous plate member 14 is disposed in the X-axis direction at a distance
from the igniter 16. The center of the first porous plate member 14 is coincident
with the axis X.
[0061] The first porous plate member 14 has an annular wall 14a formed on a peripheral edge
of a circular bottom surface 14b and is fixed by press-fitting the annular wall 14a
extended toward the igniter 16 to an inner peripheral wall surface of the cylindrical
housing 10.
[0062] As illustrated in Fig. 3, the first porous plate member 14 has a plurality of first
through holes (outer first through holes) 60 formed at an equal interval in the circumferential
direction only in the vicinity of a peripheral edge portion that is in contact with
the inner peripheral wall surface of the cylindrical housing 10. Fig. 3 shows an embodiment
such that the first through holes 60 consists of only the outer first through holes.
[0063] When r is a distance from the central point, where the axis X passes through, to
the peripheral edge portion (a radius r of the first porous plate member 14), a position
of each of the first thorough-holes 60 is set to be at about 0.1r of the length from
the peripheral edge portion 14c to the centers of the respective first through holes
60.
[0064] The first through holes 60 are formed only in the peripheral edge portion excluding
at least a region that the ignition portion 18 of the igniter 16 faces (a portion
indicated by a dot line in Fig. 3).
[0065] The first through holes 60 may be additionally formed near the inner side of the
circular bottom surface 14b (near the inner side than the outer first through holes
formed in the peripheral edge portion). In this case, the proportion of a total opening
area of only the outer first through holes formed only in the vicinity of the peripheral
edge portion with respect to a total opening area of the first through holes 60 can
be adjusted in a range between 95% and less than 100%, if additional first through
holes are provided in the inner side of the outer first through holes. The first through
holes 60 may be closed by a seal tape.
[0066] A space surrounded by the igniter 16 (the igniter 16 and the collar 17), the cylindrical
housing 10 and the first porous plate member 14 is a first combustion chamber 20.
[0067] A molded article of first gas generating agent 22 is filled in the first combustion
chamber 20 in a state of being pressed toward the igniter 16 by the first porous plate
member 14.
[0068] The molded article of first gas generating agent 22 can be in a known shape, for
example, in a cylindrical shape (including a cylindrical shape having a through hole
or a recess) or a disk-like shape (including a disk-like shape having a through hole
or a recess) as illustrated in (a) and (b) in Fig. 4.
[0069] The ignition portion 18 of the igniter 16 protrudes into the first combustion chamber
20 from an annular surface (bottom surface) 17a of the igniter collar 17.
[0070] Thereby, a pocket-like annular space 33, whose bottom surface is the annular surface
17a, is formed around the ignition portion 18 in the first combustion chamber 20.
The molded article of first gas generating agent 22 is also charged in the annular
space 33.
[0071] The annular space 33 is within a range of a height (H) from the annular surface 17a
of the igniter collar 17 to the top surface 18a of the ignition portion 18 before
activation.
[0072] The height (H) from the annular surface 17a to the top surface 18a of the ignition
portion 18 and a smallest length (Lmin) of the molded article of first gas generating
agent 22 charged in the first combustion chamber 20 satisfy a relation of Lmin<H.
[0073] A step may be formed in the annular surface 17a depending on a structure or a shape
of the igniter collar 17. In such a case, the height H may be from a deeper bottom
surface to the top surface 18a of the ignition portion 18, or may be from a higher
bottom surface to the top surface 18a of the ignition portion 18. The molded article
of first gas generating agent 22 can be arranged aslant in the annular space 33 as
long as the molded article of first gas generating agent 22 does not protrude outside
the annular space 33 in the height H direction (beyond the top surface 18a of the
ignition portion 18). The arrangement direction, shape, and dimensions thereof are
not particularly limited. The present invention includes a case where there is at
least one molded article of first gas generating agent 22 provided in the annular
space 33 in such a state.
[0074] The molded article of first gas generating agent 22, when used in a cylindrical shape
shown in (a) in Fig. 4 and in a disk-like shape shown in (b) in Fig. 4, will be described.
[0075] In the molded article of first gas generating agent 22 having a cylindrical shape
shown in (a) in Fig. 4, the smallest length (Lmin) is a diameter of an end surface
22b.
[0076] In the case of the molded article of first gas generating agent 22 having a disk-like
shape shown in (b) in Fig. 4, the smallest length (Lmin) is the thickness of the disk.
[0077] When the molded article of first gas generating agent 22 having the cylindrical shape
shown in (a) in Fig. 4, for example, is charged in the first combustion chamber 20,
a peripheral surface 22a of the molded article of first gas generating agent 22 having
the cylindrical shape may be charged in a state of abutting against the annular surface
17a of the igniter collar 17 as shown in Fig. 5.
[0078] In this case, as long as the relation of Lmin<H is satisfied, the molded article
of first gas generating agent 22 is always present inside the annular space 33 and
will not protrude out of the top surface 18a of the ignition portion 18.
[0079] A gas generating agent having a good ignition property and a good combustion maintaining
property (with a high combustion temperature) can be used as the molded article of
first gas generating agent 22.
[0080] The combustion temperature of the molded article of first gas generating agent 22
is preferably within a range of 1700°C to 3000°C.
[0081] The molded article of first gas generating agent 22 may be formed by a composition
including nitroguanidine (34% by weight) and strontium nitrate (56% by weight), for
example.
[0082] A diffuser 12 is attached to the opposite end (the other end) 10b of the cylindrical
housing 10 to form a diffuser portion.
[0083] The diffuser 12 has a substantially cup-like shape including a flange portion 12a,
a peripheral wall portion 12b, and a bottom portion 12c, and is welded and fixed to
the cylindrical housing 10 at the flange portion 12a.
[0084] A plurality of gas discharge ports 15 is formed on the peripheral wall portion 12b.
[0085] A cup-like shaped member 40 serving as the gas diverting member is disposed inside
the end (at the opposite end 10b) of the cylindrical housing 10, on the diffuser 12
side. The cup-like shaped member 40 includes a bottom surface 40a and a peripheral
wall portion 40b. The peripheral wall portion 40b is provided with a plurality of
communication holes 40c. A projection 40d is formed at a central part of the bottom
surface 40a so as to extend toward the igniter 16.
[0086] The cup-like shaped member 40 is fixed by a known method (welding or the like) to
the flange portion 12a of the diffuser 12. An opening of the cup-like shaped member
40 is closed by a seal tape 45 so that moisture from the gas discharge ports 15 is
prevented from entering.
[0087] An outer diameter of the cup-like shaped member 40 is smaller than an inner diameter
of the cylindrical housing 10. Therefore, a gap 36 exists between the peripheral wall
portion 40b and the inner peripheral wall surface of the cylindrical housing 10, and
comes to a dead end at the flange portion 12a of the diffuser, forming a pocket portion
(gap) 36. The pocket portion 36 is continuous with a cylindrical gap 35 and functions
to retain the particulate in combustion gas.
[0088] A second combustion chamber 25 is provided in the cylindrical housing 10 between
the diffuser 12 (the cup-like shaped member 40) and the first combustion chamber 20
(the first porous plate member 14).
[0089] The second combustion chamber 25 is surrounded by the cylindrical member 30, the
second porous plate member 32 and the inner peripheral wall surface of the cylindrical
housing 10. A molded article of second gas generating agent 50 is charged in the second
combustion chamber 25.
[0090] The cylindrical member 30 includes a peripheral wall portion 30a having a smaller
outer diameter than the inner diameter of the cylindrical housing 10, and a cylindrical
gap 35 having a uniform width is formed between the peripheral wall portion 30a and
the cylindrical housing 10.
[0091] In the cylindrical member 30, a plurality of gas passage holes (communication holes)
37 are formed axially at equal intervals on the peripheral wall portion 30a. The gas
passage holes 37 are formed at equal intervals in the circumferential direction of
the cylindrical member 30 (the peripheral wall portion 30a). The second combustion
chamber 25 and an annular gap 35 communicate with each other through the gas passage
holes 37. Note that the gas passage holes 37 may be unevenly distributed closer to
the diffuser portion 12 on the peripheral wall portion 30a. Further, the gas passage
holes 37 may be formed so that the opening area thereof increases toward the diffuser
portion 12.
[0092] The cylindrical member 30 has, in a first opening end thereof, an enlarged diameter
portion 31 formed in a flange-like shape on the side of the igniter 16. An outer peripheral
edge 31a of the enlarged diameter portion 31 abuts against the inner peripheral wall
surface of the cylindrical housing 10.
[0093] An outer diameter of the outer peripheral edge 31a is slightly larger than the inner
diameter of the cylindrical housing 10 before the cylindrical member 30 is disposed
inside the cylindrical housing 10. When the cylindrical member 30 is disposed inside
the cylindrical housing 10, the cylindrical member 30 is press-inserted to the inner
peripheral wall surface of the cylindrical housing 10 due to the resilience of the
enlarged diameter portion 31. Therefore, a gap is not formed in the press-fitted portion.
Further, in order to fix the cylindrical member 30, a step that fits into an opening
peripheral edge of the enlarged diameter portion 31 or a projection that engages with
the opening peripheral edge may be formed on the inner peripheral wall surface of
the cylindrical housing 10.
[0094] In the cylindrical member 30, a central hole 30d is formed at a central portion of
a bottom surface 30b on the side of the diffuser portion 12 (a second end of the cylindrical
member 30). The central hole 30d is fitted to the projection 40d formed on the bottom
surface 40a of the cup-like shaped member 40.
[0095] Since the enlarged diameter portion 31 is press-fitted to the inner peripheral wall
surface of the cylindrical housing 10 and the central hole 30d is fitted to the projection
40d of the cup-like shaped member 40, the cylindrical member 30 is fixed in both the
axial direction and the radial direction and is disposed on the same X-axis as the
cylindrical housing 10.
[0096] The second porous plate member 32 is disposed at a distance (for example, approximately
3 mm to 20 mm) in the X-axis direction from the first porous plate member 14, and
the center of the second porous plate member 32 is coincident with the axis X.
[0097] The second porous plate member 32 has an annular wall 32a which is formed on a peripheral
edge of a circular bottom surface 32b so as to extend toward the igniter 16. The second
porous plate member 32 is fixed by the annular wall 32a press-inserted to the inner
peripheral wall surface of the cylindrical housing 10.
[0098] A space 19 is formed between the second porous plate member 32 and the first porous
plate member 14. A volume (the gap between the first and second porous plate members
14 and 32) of the space 19 changes depending on a shape and an amount of each of the
molded article of the gas generating agent 22 and 50 charged in the respective combustion
chambers 20 and 25.
[0099] Second through holes 65 of the second porous plate member 32 are openings smaller
than the molded article of second gas generating agent 50. The second through holes
65 may be closed by a seal tape.
[0100] An arrangement of the second through holes 65 of the second porous plate member 32
is not particularly limited, and a preferred embodiment will be described with reference
to Fig. 6.
[0101] Fig. 6 shows the second porous plate member 32 seen from the diffuser portion 12
of Fig. 1. The first through holes 60 are depicted by dot lines because the first
porous plate member 14 is completely concealed by the second porous plate member 32.
- (a) in Fig. 6 shows a state where the first through holes 60 and the second through
holes 65 do not face each other in the X-axis direction.
[0102] This does not indicate that the first through holes 60 in Fig. 3 and the second through
holes 65 in (a) in Fig. 6 are arranged differentially. These holes are formed in the
same manner on each of the respective porous plate member, however, arranged circumferntially
inconsistent with each other when provided inside the cylindrical housing 10, so that
the first through holes 60 and the second through holes 65 does not face each other.
[0103] The first through holes 60 and the second through holes 65 can be arranged to face
each other in the X-axis direction, or part of the respective through holes 60 and
65 can overlap in the X-axis direction.
[0104] The second porous plate member 32 in (a) of Fig. 6 is preferable, when combined with
the cylindrical member 30, because ignition of the molded article of second gas generating
agent 50 existing in the vicinity of the peripheral wall portion 30a of the cylindrical
member 30 is accelerated so that the gas discharge passage is opened quickly.
[0105] Moreover, for example, as shown in (b) in Fig. 6, the second through holes 65 can
be formed only in a central portion (the portion located radially further inside than
the first through holes 60) in the second porous plate member 32, excluding the peripheral
edge portion in contact with the inner peripheral wall surface of the cylindrical
housing 10.
[0106] When the second through holes 65 are arranged as shown in (b) in Fig. 6, the positions
of the first and second through holes 60 and 65 do not overlap in the X-axis direction.
[0107] Furthermore, for example, as shown in (c) in Fig. 6, the formation positions of the
second through holes 65 shown in (a) and (b) in Fig. 6 can be combined.
[0108] The molded article of second gas generating agent 50 uses a gas generating agent
having a lower combustion temperature than the molded article of first gas generating
agent 22. The combustion temperature of the molded article of second gas generating
agent 50 is preferably within a range of 1000°C to 1700°C. The molded article of second
gas generating agent 50 can be in a single perforated cylindrical shape having an
outer diameter of 1.8 mm, an inner diameter of 0.7 mm and a length of 1.9 mm, and
include guanidine nitrate (41% by mass), basic copper nitrate (49% by mass), a binder
and an additive.
[0109] The molded article of second gas generating agent 50 is charged in a state of being
pressed by the second porous plate member 32 toward the diffuser portion 12. Thereby,
the molded article of second gas generating agent 50 is densely charged in the second
combustion chamber 25 and the formation of a gap is prevented.
[0110] A ratio (a2/a1) of a total opening area (a2) of the second through holes 65 formed
in the second porous plate member 32 to a total opening area (a1) of the first through
holes 60 formed in the first porous plate member 14 is preferably between 0.9 and
1.2, and more preferably between 0.95 and 1.1.
[0111] Next, operations of the gas generator shown in Fig. 1 will be described.
[0112] When the igniter 16 is activated, a central portion of the ignition portion 18 starts
breaking and combustion products generated therefrom collides with a surface of the
first porous plate member 14 where the first through holes 60 are not formed, and
part of the combustion products diffuses toward the outer side in the radial direction
and the collar 17.
[0113] When the first porous plate member 14 of the present invention is used, the combustion
products reflect by striking the central portion (the portion where the first through
holes 60 are not formed or the portion where the opening area of the first through
holes 60 is small) in the first porous plate member 14 so that the combustion products
can easily reach the molded article of first gas generating agent 22 filled in the
pocket-like annular space 33.
[0114] As a result, the entire molded article of first gas generating agent 22 in the first
combustion chamber 20 ignites easily.
[0115] When the internal pressure of the first combustion chamber 20 increases with the
combustion products (flames and high-temperature gas) generated from the molded article
of first gas generating agent 22, the seal tape closing the first through holes 60
is broken so that the combustion products flow into the space 19 therethrough.
[0116] The combustion products flowing into the space 19 flow into the second combustion
chamber 25 through the second through holes 65 of the second porous plate member 32
to ignite and burn the molded article of second gas generating agent 50.
[0117] The combustion gas and the combustion products generated in the second combustion
chamber 25 flow into the cylindrical gap 35 via the gas passage holes 37 and collide
with the inner peripheral wall surface of the cylindrical housing 10.
[0118] As a result, the flow is directed toward the diffuser 12. During this process, residues
contained in the gas adhere to the inner peripheral wall surface of the cylindrical
housing 10.
[0119] Furthermore, the combustion gas and the combustion products strike the flange portion
12a of the diffuser portion 12 thereby changing the flow direction thereof, and enter
the cup-like shaped member 40 through the communication holes 40c. After that, the
combustion gas and the combustion products strike the bottom portion 12c of the diffuser
12 thereby changing the flow direction thereof again, and are discharged from the
gas discharge ports 15.
[0120] Since the first and second porous plate members 14 and 32 are press-inserted to the
cylindrical housing 10, even though the porous plate members may move in the X-axis
direction due to the pressure during activation, because of a gap, corresponding to
the length of the annular wall 32a, maintained between the first and second porous
plate members 14 and 32, the space 19 is thus maintained.
[0121] When the second porous plate member 32 as shown in (a) in Fig. 6 is used in the gas
generator in Fig. 1, the following advantageous effects are obtained.
[0122] Although the gap 35 serving as a gas discharge passage is formed by the cylindrical
member 30 disposed in the cylindrical housing 10, the gap 35 is not formed on the
side of the second porous plate member 32.
[0123] When the second porous plate member 32 provided with the second through holes 60
arranged in the peripheral edge portion as shown in (a) in Fig. 6 is used, the combustion
products are discharged in the direction along the peripheral wall portion 30a of
the cylindrical member 30, and therefore, the molded article of second gas generating
agent 50 near the gas passage holes 37 is preferentially combusted.
[0124] As a result, since a gas discharge passage between the second through holes 65 and
the gas passage holes 37 (the gas passage holes 37 closest to the second porous plate
member 32) is formed in the second combustion chamber 25 promptly, gas is discharged
from the housing 10 reliably and quickly.
[0125] When the second porous plate member 32 as shown in (b) in Fig. 6 is used in the gas
generator in Fig. 1, a molded article of second gas generating agent 50 in part facing
the second porous plate member 32 is more likely to be combusted uniformly. As results,
combustion of the second combustion chamber 25 starts in advance in the end surface
in the axial direction on the side of the second porous plate member 32.
[0126] When the second porous plate member 32 as shown in (c) in Fig. 6 is used in the gas
generator in Fig. 1, both effects of the second porous plate members 32 shown in (a)
and (b) in Fig. 6 are obtained.
[0127] The invention thus described, it will be obvious that the same may be varied in many
ways. Such variations are not to be regarded as a departure from the spirit and scope
of the invention, and all such modifications as would be obvious to one skilled in
the art are intended to be included within the scope of the following claims.